It is now more common to find wind turbine farms as one tours the United States. For example, large wind energy farms are located in the United States in Texas, Indiana and California. Wind energy farms are now found world-wide from Spain to Australia and are providing an increasing percentage of the world's energy requirements. Sizes of structures supporting wind turbines have evolved from, for example, 0.15 MW sized wind turbines with blades having approximately a 26 foot (approximately eight meter) diameter to 5 MW generators having rotor blades of over 100 meters in diameter. A typical wind turbine is shown in FIG. 1 and will now be discussed in some detail.
A wind turbine for mounting on a sufficiently high tower is shown in FIG. 1 as turbine 100. A variable speed rotor 105 may turn a gearbox 108 (lower block diagram), 112 (black and white drawing) to increase the rotational velocity output of the rotor and blade assembly 105, 107, 109. For example, a so-called cut-in rotational velocity of a rotor 105 may be about six revolutions per minute and the rotor blade may typically cut-out at about 30 revolutions per minute by controlling the pitch of the rotor via pitch system 107 during conditions of high wind velocity and to reduce rotor blade noise. Typically, wind speeds over 3 meters/sec are required to cause the large rotor blades to turn at the cut-in rotational velocity. Wind frequency between cut-in and cut-out velocities has been measured to vary depending on location, weather patterns and the like. Placement high on a hill or a mountain of a wind turbine, for example, may be preferable to locating the wind turbine at a low point in a valley. Consequently, it may be recognized that there are periods of time when wind turbines 100 do not have sufficient wind speed to operate at all depending on weather conditions, placement and the like.
When wind speed reaches an excess amount, a pitch (and yaw) control system 107 may measure the wind speed and adjust pitch of rotor blades 105 to pass more wind and so control the rotor blade from turning too fast as well as point the rotor blade into the wind. Yaw control may supplement pitch control to assist in pointing a rotor into the direction of flow. Noise from rapid rotor velocity can be abated, for example, by turning the blade parallel to the wind using a wind speed control system to thus maintain the rotational velocity close to a cut-out speed. An anemometer 180 at the tail of the turbine 100 measures wind velocity and provides a control input. The tail of the turbine may be equipped with a rudder or wind vane for pitch or yaw control. Horizontal or vertical stabilizers (not shown) maybe provided for pitch or yaw control. The rudder or wind vane may help point the variable speed rotor 105 into the wind. In general, however, there is a problem with known wind turbine systems that only a portion of the wind energy available at a site of a wind turbine farm may be harnessed resulting in harnessing only a portion of the kinetic energy of the available wind to feed a power grid.
Referring again to FIG. 1, the gearbox 108, 112 may multiply the cut-in rotor output of six RPM, for example, by fifty yielding 300 RPM (more or less) for turning a variable speed generator 110, 114. A variable speed generator 110 (block diagram), 114 (black and white line drawing) may be used to convert the varying rotational speed of a main shaft (shown to the left of the man) to a variable power alternating current 122 for input to a power converter called a variable frequency converter 120 (VFC 120). In so doing, the variable frequency alternating current power 122 may be converted to direct current 124 and then to irregularly switched alternating current power 126. The conversion from variable frequency to direct current to constant frequency introduces inefficiency in converting flow energy to useable electric energy and so reduces an amount of power that could be output to grid 130.
VFC 120 converts variable power alternating current 122 produced by variable speed generator 110 to direct current DC 124, to irregular switched alternating current 126. The irregular switched alternating power 126 is acceptable for outputting to grid 130 of constant power alternating current at constant frequency 128 but is inefficiently produced. The cost to replace known variable frequency converters (power converters) 120 is, for example, between $50,000 and $100,000 and, consequently, an alternative design has been sought for the conventional wind turbine 100 of FIG. 1.
A gearbox 108, 112 is known to have a failure rate of approximately 5%. Electronics used in a wind turbine 100 has the highest potential failure rate of 26%. Control units generally exhibit a failure rate of 11%. Sensors and yaw control exhibit approximately a 10% failure rate. The failure rate of VFC 120 may be on the order of 26% (electronics) according to an ongoing consortium's study of drive train dynamics at the University of Strathclyde, Glasgow, Scotland. The mean time between failures may be only two years on average; and the replacement cost may be over $50,000 (US) per converter. A failure rate of the generator 110, 114 is on the order of 4.5%. Consequently, problems related to known wind turbines relate closely to the failure rate of gearboxes, generators, variable frequency converters and associated electronics and inefficiencies of operation.
A solution to the identified problems is to provide a constant rotational velocity as an input to the electric generator so that the generator in turn can produce a constant output at constant frequency directly to grid 130. Transmissions have been developed or are under development by the following entities: IQWind, Fallbrook and Voith Wind (Voith Turbo) to provide a constant output from a variable input. U.S. Pat. No. 7,081,689, (the '689 patent) assigned to Voith Turbo of Germany is exemplary of an overall system control design providing three levels of generator control. Voith provides a so-called power split gear and a hydrodynamic Fottinger speed converter or transformer adapted to be connected between a rotor and gear assembly and a synchronous generator for outputting power to a grid, for example, at 50 Hz (European). As discussed at col. 2, lines 60-67, “The invention is based on the object of providing a control system for a wind power plant, which allows the operation of a speed-constant, mains-coupled generator in conjunction with an efficiency-optimized speed guidance of the wind rotor for the partial load range.” A further control system is provided for “speed reduction for noise limitation and for full load operation.” As shown in FIG. 1, the wind speed and rotor revolution speed are sensed as inputs to control several operating states: power generation, synchronization, braking, load shedding and voltage drop. In particular, a controller is provided for controlling rotor blade angle, a controller is provided for determining the speed of the generator via an input to the hydrodynamic converter, and the synchronous generator is controlled according to requirements from the electric grid, voltage, frequency, power and reactive power.
The '689 patent provides considerable guidance into the variable factors influencing wind turbine behavior and how to control them. FIG. 3, for example, provides a graph of cut-in and cut-out revolution speed of a rotor versus rotor power in kW and rotor torque. In particular, FIG. 3 shows a set of solid line curves for power taken up by a wind rotor at wind speeds between 8 m/s and 18 m/s. It further shows broken line curves for how a synchronous generator may provide torque in a range between 10 kNm to 35 kNm depending on torque characteristics and associated parabolics. The respective power maxima are situated on a parabolics (power) curve. FIG. 4 shows power in kW, revolution speed of the rotor and speeds in the hydrodynamic drive train. FIG. 5 shows related power, optimal revolution speed and how to set the reaction member for the hydrodynamic drive train. FIG. 7 provides a ten minute (600 second) wind profile where the average wind speed is 11 m/s and the turbulence intensity is at 17.2%. The wind velocity can vary from 6 to 15 m/s, the rotor torque can vary from 0 to 2×106 N/m when a brake cuts in. The torque on the main shaft can reach a level of 16×106 when the revolution speed of the rotor may be stopped. The rotor blade angle may vary over time and the reaction member controlled accordingly.
A problem with the Voith system represented by the '689 patent is its use of hydraulics and resultant potential toxicity. Moreover, it appears to be inefficient compared with other known systems.
IQWind of Israel is represented by U.S. Patent Application Publication No. 2009/0118043 published May 7, 2009. A variable dynamic gear is shown and described for use in power generators, per paragraph [0004], “where it may be preferable to maintain a constant output speed despite variations in the power of a source of mechanical power being harnessed.” A pair of cones are described which provide the variable dynamic gear—in one embodiment with a stepped surface and in another embodiment with a smooth surface. While described as dynamic and variable, it is respectfully submitted that IQWind provides a fixed number of speeds and may be inefficient and expensive to maintain and install. IQ Wind may rely considerably on electronic control which may result in a high failure rate.
Fallbrook Technologies of San Diego, Calif. provides a continuously variable transmission as disclosed, for example, in US Patent Application Publication No; 2008/0132373 published Jun. 5, 2008. According to the ABSTRACT, an infinite number of speed combinations are provided. Nevertheless, the transmission depicted in FIG. 1 appears to be unscalable whereby a plurality of speed adjusting balls are utilized to adjust speed between input and output. Thus, it is respectfully submitted that the Fallbrook solution appears to be unscalable and may be expensive to install and maintain.
While IQWind, Fallbrook and Voith appear to provide a constant output from a varying input, the described transmissions appear to relate closely to wind flow and do not provide discussion of the problem of other liquids such as water flow from, for example, river, ocean tidal and wave motion. Gutsfeld, U.S. Pat. No. 4,104,536, provides an example of a stream or river-powered turbine with radially-extending vanes, reminiscent of the paddle wheels of stone mills of the nineteenth century. Rauch, U.S. Pat. No. 4,524,285, provides an example of a hydro-current energy converter. Conical members direct the water flow to a rotor and the whole device May be mounted to the sea floor via a tripod. Ruiz et al., U.S. Pat. No 5,834,853, describes a sea or river powered power plant having a ratchet-type turbine. Waves and currents strike the lower portions thereof to turn a shaft of a generator. Szpur, U.S. Pat. No. 5,946,909, describes a floating, turbine system whereby a plurality of turbine rotors operate in series connection across a span of water from shore to a fixed location in the water to operate a land-based generator. Carillo, U.S. Pat. No. 6,396,162, describes an underground hydroelectric plant which uses an underground water tank connected to several penstocks, which, in turn, carry the water to generators for generating electricity. Rembert, U.S. Pat. No. 6,861,766; describes a hydro-electric power system that further includes a wind turbine. Rembert thus considers the use of both water pumped to a height and wind for generating electric power. Mondl, U.S. Pat. No. 7,442,002, describes a tidal turbine installation chained to the river floor but permitted to float and generate electric power from the water current flowing through the device. Mondl describes a problem at high water of floating debris, not considered by Szpur, which, it is respectfully submitted, may catch floating debris.
Water is considerably more dense than air and requires less of a flow speed to generate appreciable electric current flow. On the other hand, similar problems as are found in wind turbine present themselves with water flow turbines. The rotor blade or radial vane must be controlled, for example, to face the current. Ideally, it is known that water flows fastest at the center of a stream, a creek, a tidal area, a wave and the like. An ocean wave proximate a beach has unique characteristics of high velocity movement as the wave crashes and strong undercurrents as the wave retreats from the shore. There is maintained a requirement for a variable input constant output regardless of water flow application where water has the advantage of increased density. Consequently, there is no need for, for example, 100 meter diameter rotor blades to capture the kenetic flow energy.
While harnessing of wind and water and other flow energy enhances a clean environment, there remains a need in the art to extend the concept of variable input and constant output to provide a flow energy system that promotes greater efficiency with higher energy output, at lower cost and at lower failure rate.
Each of the above-identified patents and published patent applications should be deemed to be incorporated by reference herein as to their entire contents.